Fluidic circuit control for centering sanding belt on a belt sander

ABSTRACT

An abrasive belt is supported on a pair of rolls, at least one of which is steerable to control lateral travel of the belt. A control bar over which the underside of the belt travels is provided with one or more sensing apertures connected to fluidic circuitry which actuates the steering mechanism to control the lateral position of the belt and to cause the belt to oscillate laterally. The circutry is such that the sensing of belt position is accomplished entirely by air emerging from control apertures without entering another aperture.

United States Patent 1 Robinson July 17, 1973 FLUIDIC CIRCUIT CONTROL FOR CENTERING SANDING BELT ON A BELT SANDER [76] Inventor: Charles E. Robinson, 208 Gardner Ave., Burlington, Wis. 53105 [22] Filed: Feb. 17, 1971 [2]] Appl. No.: 115,960

[52] US. Cl. 51/135 RT [51] Int. Cl B24b'21/00 [58] Field of Search 51/135, 135 HT, 143

[56] References Cited UNITED STATES PATENTS 2,587,603 3/1952 Czarnecki 51/135 BT 3,008,276

11/1961 1 Kile 51/135 BT 3,552,067 1/1971 Przygocki 51 135 B'l" Primary Examiner-Othell M. Simpson Attorney-Wheeler, House & Wheeler [57] ABSTRACT An abrasive belt is supported on a pair of rolls, at least one of which is steerable to control lateral travel of the belt. A control bar over which the underside of the belt travels is provided with one or more sensing apertures connected to vfluidic circuitry which 'actuates the steering mechanism to control the lateral position of the belt and to cause the belt to oscillate laterally. The circutry is such that the sensing of belt position is accomplished entirely by air emerging from control apertures without entering another aperture.

10 Claims, 7 Drawing Figures FLUIDIC CIRCUIT CONTROL FOR CENTERING SANDING BELT ON A BELT SANDER SUMMARY OF THE INVENTION My invention provides a new fluidic abrasive belt control mechanism including novel control bars and a novel fluidic circuit composed of known fluidic circuit elements, to provide a device in which the belt passes over a control bar located entirely at the inner side of the belt, in which air exits from, but does not enter, sensing apertures immediately ajacent to the abrasive belt, in which control of lateral belt position is readily accomplished by persons who are not highly skilled, in which belt oscillation laterally of the roll is automatically provided for, and in which no part of the sensing mechanism is in the plane of belt movement regardless of how far the belt moves, thus eliminating a source of damage to the sensing mechanism and to the belt.

The control bar removes the edge curl from that portion of the belt which is being sensed, increasing the accuracy of sensing and permitting the use of sensing elements which have a single aperture to emit air. These replace devices having U-shaped throats in which the sensing port was an entrance for air from a jet across the throat. The sensitivity of the old device varied with the edge curl on the belt, and dirt was apt to block or partially block the port. If the belt moved too far, it struck the throat of the sensor, damaging both.

In my device air is only emitted from the sensing apertures. No part of the control bar extends into the plane of the belt. The fluidic circuit elements associated with the apertures respond to back pressure in the aperture, both in the device of FIG. I and in the somewhat different cone jet devices of FIGS. 6 and 7 which are never wholly blocked.

Depending on the range of oscillation desired for the belt, I may use a pair of sensors with the belt between, and a bi-stable circuit element to respond to them, or a single sensor at one edge of the belt and a monostable fluidic circuit element to respond to it. I find it advantageous to add an amplifier and a pilot operated valve to operate the known belt roll steering mechanism. Many combinations are possible using these principles.

DESCRIPTION FIG. I is a highly schematic perspective view of a sanding machine, including a schematic fluidic control circuit.

FIG. 2 is a cross-sectional view on line 2-2 of FIG. 1 showing the control bar of FIG. 1.

FIG. 3 is a view similar to FIG. 2 showing a modified control bar.

FIG. 4 is a view similar to FIG. 2 showing a modified control bar.

FIG. 5 is a perspective view showing details of the manner in which an actual sanding machine may be controlled by the circuit of my invention.

FIG. 6 is a cross-sectional view through the control bar of FIG. 3 showing the manner in which a cone jet is mounted therein.

FIG. 7 is an enlarged view similar to FIG. 6 showing the cone jet in association with a modified fluidic circuit particularly adapted for use therewith.

The following description is sufficiently detailed to show the manner in which my invention may be carried out, by way of exemplification rather than limitation.

The scope of my invention is defined in the claims appended hereto.

As generally shown in FIG. 1, the device to which my invention is applied is a sanding machine having a sanding belt 10 extending over a pair of rolls Ill and 12, one of which is steerable. The belt drive is not shown. As shown in FIG. 1 the steerable roll is roll 12. The steering mechanism is schematically represented by pivotable yoke 13 and double acting pneumatic cylinder 14 acting on the yoke 13 in such a direction as to displace the axis of roll 12 in opposite directions so as to cause the belt to move laterally with respect to the roll. This adjustment is utilized to maintain the belt in a desired average position with respect to roll 12 and to oscillate the belt laterally with respect to roll 12.

FIG. 5 shows a machine configuration more in accord with that which would be found in an actual machine. The steerable yoke 13 is pivoted at 15 to a frame 16 which is held in a fixed orientation. The double acting cylinder 14 is pivotally mounted on a rod 17 which is carried on a movable member 18. Adjustment bolts 19 fix and adjust the position of member 18 in the direction in which cylinder 14 is actuated. The piston of cylinder 14 may advantageously be provided with a piston rod 20 at each end connected to yoke 13. Member 18 may be pivoted at 21 to fixed frame 16.

In the form of my device shown in FIGS. 1 and 2, the belt 10 is underlaid by a control bar 30 having a curved upper surface 31 over which the belt passes. The surface may be covered with an anti-friction material, preferably one having high resistance to wear because although the non-abrasive inner sideof belt 10 is in contact with surface 31, even that surface of belt 10 produces a high rate of wear on conventional metal surfaces.

Bar 30 is provided with a series of sensing apertures 32. As shown in FIG. 1 air is suppied to a pair of apertures 32 (one on each side of the belt) by conduits 33 and 34. The particular pair of apertures 32 selected will define the limits of lateral movement of belt 10 on rolls I1 and 12, and accordingly the amount of lateral movement permitted to belt 10 may be controlled simply by selecting an appropriate pair of apertures 32. Actual control over the movement of belt 10 is maintained by a novel fluidic control circuit which may take several forms. As disclosed in FIG. 1, the control circuit includes a pair of fluidic sensing modules 35 such as those supplied by Corning Glass Co. These have the characteristic that air entering at port 36, labelled air supply, normally emerges at port 380 and directs a sensing signal to aperture 32. When aperture 32 is covered this signal switches the exhaust to port 38 and it is carried by respective conduit 39 or 40 to a bi-stable fluidic circuit device 41. When aperture 32 is uncovered by the belt 10, the air exhaust returns to port 380.

Fluidic circuit module 41 is a bi-stable flip-flop device. That is, it remains in either of two stable output modes indefinitely in the absence of input signals through ports 39 and 40. Air supplied at port 42 emerges either from port 43 or port 44 tp be carried down respective air conduits 45 or 46 to the next fluidic circuit module. Air supplied at control port 47 from conduit 39 causes the output flow to emerge at port 44, while air supplied to control port 48 through conduit 40 causes the output to emerge from port 43. Once the output flow is emerging from a particular output port, it will continue to do so as long as the device is operated, unless a control pressure switches it to the other output mode.

Fluidic module 50 is an amplifier module. It is also bi-stable. The air supply is at port 51 and the outputs at ports 43 and 44 of module 41 are applied to respective control ports 52 and 53 of amplifier module 50 to switch the output flow from port 54 to 55 or vice versa. The air output is greater than that from module 41. The air that emerges from port 54 or 55 is carried by conduits S6 and 57 to respective operating ports 58 and 59 of a pilot operated valve 60. Valve 60 switches the air supplied at 61 to conduit 62 or 63 to actuate respective ends of double-acting cylinder 14.

In operation this circuit will provide continuous actuation of cylinder 14 to displace the axis of roll 12 in one direction or the other from a position parallel to the axis of roll 11 until the direction of actuation of cylinder 14 is reversed by the action described above. Belt will then reverse its lateral travel and uncover the respective orifice 32, but the uncovering of the orifice will not produce a change in the output mode of fluidic module 41. Since that module is bi-stable, it will remain in one output mode until a control signal is received from the other sensor module 35, produced when belt 10 covers the aperture 32 which is connected to that module. Thus belt 10 will travel laterally back and forth between the two selected apertures 32 to which sensor modules 35 are connected. This lateral oscillation, which produces a better finish on a work piece being abraded by the belt 10, is both produced and controlled by the fluidic circuit. The use of the fluidic circuit described has the additional advantage that the control provided by air emerging from apertures 32 is extremely insensitive to dirt and vibration.

The fluidic circuit shown in FIG. 7 is another example of a control circuit which may be used within my invention. It is used with a single sensing device 80 having one aperture 81 at one side of belt 10. That sensing device is preferably of the type known as a cone jet. Control bar 30 is not appropriate for the mounting of such a sensor and accordingly modified bars 70 or 75 are used as shown respectively in FIGS. 3 and 4. Both bars are provided with curved upper surfaces 31. In the case of bar 70 surface 31 is provided with a linear series of apertures 71 and the lower surface is provided with a corresponding series of apertures 72 in which the cone jet 80 is mounted (as best shown in FIGS. 3 and 6). In control bar 75 (FIGS. 4 and 7) the apertures 71 are replaced by a slot 76 and apertures 72 are replaced by slot 77 providing continuous positioning of cone jet 80.

Cone jet 80, as shown in FIG. 7, is mounted in bar 70 or 75 with the jet aperture 81 just out of contact with belt 10, which follows surface 31. This is accomplished with a pair of mounting nuts 82 on the threaded body of cone jet 80. Nuts 82 grip the opposite sides of openings 72 or of slot 77.

Cone jet 80 is provided with an air supply conduit 83 and with an output conduit 84. When air is supplied through conduit 83 a cone of air emerges at orifice 81. There is no output to conduit 84 unless belt 10 moves to cover orifice 81, in .which event the air emerging from orifice 81 is partially blocked causing an output through conduit 84 due to back pressure. This output is supplied to fluidic module 90 which is a monostable device having an air supply port 91, a control port 92 which receives air from conduit 84, a principal outlet port 93 and auxilliary outlet port 94. Principal outlet port 93 supplies outlet air to conduit 95 whenever no air is supplied at port 92. Outlet port 94 supplies air to conduit 96 only when air is supplied to port 92 by conduit 84. Other fluidic proximity sensors may be used in this manner.

As in the circuit shown in FIG. 1, an amplifier module 50 is provided so that the output at ports 54 and 55 is sufiicient to operate pilot operated valve 60 which controls cylinder 14. Although amplifier module 50 is a bi-stable device, it is controlled by sensor module 90 which is monostable. The result is that whenever belt 10 moves into the zone of influence of air emerging from aperture 81, a control signal flow of air is produced in conduit 84 which switches the output of module 90 to outlet port 94. This in turn switches amplifier module 50, reversing pilot operated valve 60. Cylinder 14 then steers the axis of roll 12 in a direction causing belt 10 to move laterally away from aperture 81. As belt 10 moves away from aperture 81, monostable module 90 ceases to receive air through conduit 84 and returns to its stable primary output mode in which output air emerges at port 93. This switches amplifier module 50 to its other output mode, reversing valve 60 and actuating cylinder 14 in the opposite direction. The axis of cylinder 12 shifts in a direction which causes abrasive belt 10 to move laterally toward aperture 81. Thus belt 10 oscillates laterally within a very narrow range of movement just at the edge of the jet of air emerging from aperture 81. The lateral position of the belt can be set simply by positioning cone jet 80 within control bar or 75, without the need of an additional cone jet at the other edge of belt 10. Moreover, because belt 10 never actually touches the physical structure of cone jet 80 it is long lasting. The cone jet itself is a commercial device, as are the various fluidic modules described.

The cone jet 80 is mounted just below surface 31 and just out of contact with belt 10 to avoid wear. The mounting position must be close enough to the belt to provide substantial back pressure to provide the control signal. The correct distance may vary with the size of the cone jet, the air supply pressures, and the characteristics of the monostable fluidic module, but is readily determined for a particular combination. Some monostable fluidic elements may be adjusted, or biased, to operate on larger or smaller control port air signals.

These and other similar devices may be used in carrying out my invention which is defined in the following claims.

What is claimed:

1. In a machine having rolls, an abrasive belt driven around the rolls, and means for displacing the axis of one of the rolls to alter the lateral postion of the belt on the rolls, the improvement comprising:

a control bar having an upper surface in contact with the inner surface of said belt, an air aperture in said upper surface of said control bar, control means connected to supply air to said aperture and including pneumatic logic circuit means including means to actuate said means for displacing the axis of one of the rolls responsive solely to the covering of said aperture by said belt to displace the axis of said roll in a first direction to cause said belt to move laterally in a direction to uncover said aperture, said control means including means to maintain the displacement of said axis in said first direction until a predetermined lateral displacement of said belt has occurred, said control means being further provided with connections to said means for displacing the axis of said one of said rolls effective to cause said means for displacing the axis to displace the axis of said roll in a second direction upon occurrence of said predetermined axial displacement of said belt to cause the belt to move laterally toward said air aperture.

2. The device of claim 1 in which a second air aperture is provided on said control bar at the other edge of said abrasive belt from said first opening, said second air aperture comprising part of the means to predetermine the lateral displacement of said belt prior to reversal, said logic circuit means including means to cause air flow in an output circuit only when said second aperture is covered, and means connecting said output circuit to said means for displacing the axis of one of the rolls to cause said means for displacing the axis of one of the rolls to cause displacement of said roll in said second direction upon covering of said second aperture by said abrasive belt.

3. The device of claim 2, said logic circuit including a bi-stable fluidic circuit element having two output ports which respectively emit air as a stable output mode after an associated control port has been supplied with air, and two control ports respectively connected to said fluidic circuit element to initiate said respective stable output modes when the respective inputs receive air, said logic circuit further including a respective fluidic circuit element connected to each said air aperture to supply said air to its respective control port only when said aperture is covered by said belt, the respective output ports of said fluidic circuit element being the portion of said logic circuit connected to said means for displacing the axis of one of the rolls, one said output port being connected to cause said displacement of one of the rolls in said first direction and the other said output port being connected to effect displacement in said second direction whereby each stable output mode causes displacernt of said belt in a respective direction.

4. The device of claim I in which said predetermined lateral displacement is predetermined solely by the uncovering of said aperture by said abrasive belt.

5. The device of claim 4 further including a monostable fluidic circuit element having one stable output mode and one unstable output mode and having an input port connected to initiate said unstable output mode only while said input port is receiving air, and means to supply air to said input port only when said belt moves laterally to partially block said aperture, each said output mode being connected to cause displacement of said roll axis in a respective direction.

6. The device of claim 5 in which said aperture is the outlet of a cone jet.

7. The device of claim 1, said control bar having a curved upper belt-contacting surface, said bar having a plurality of apertures extending through said surface at each edge of said belt, said apertures being selectively connectable to said control means to predetermine the limits of lateral displacement of said belt.

8. The device of claim 11, said control bar having a curved upper belt-contacting surface, said bar being further provided with means for mounting a sensing unit containing said air aperture just out of contact with said surface and said belt, the mounting of said sensing unit being effective to predetermine the limits of lateral displacement of said belt.

9. The device of claim 8, said mounting means including discrete mounting openings in the rear surface of said bar, and clamp means onsaid sensing unit to secure said unit in a selected aperture, said upper surface being interrupted above each mounting opening.

10. The device of claim 8, said mounting means including a longitudinal slot in the rear surface of said bar, and clamp means on said sensing unit-to secure said unit to the margins of said slot in a selected longitudinal position, said upper surface of said bar being interrupted at least above said position. 

1. In a machine having rolls, an abrasive belt driven around the rolls, and means for displacing the axis of one of the rolls to alter the lateral postion of the belt on the rolls, the improvement comprising: a control bar having an upper surface in contact with the inner surface of said belt, an air aperture in said upper surface of said control bar, control means connected to supply air to said aperture and including pneumatic logic circuit means including means to actuate said means for displacing the axis of one of the rolls responsive solely to the covering of said aperture by said belt to displace the axis of said roll in a first direction to cause said belt to move laterally in a direction to uncover said aperture, said control means including means to maintain the displacement of said axis in said first direction until a predetermined lateral displacement of said belt has occurred, said control means being further provided with connections to said means for displacing the axis of said one of said rolls effective to cause said means for displacing the axis to displace the axis of said roll in a second direction upon occurrence of said predetermined axial displacement of said belt to cause the belt to move laterally toward said air aperture.
 2. The device of claim 1 in which a second air aperture is provided on said control bar at the other edge of said abrasive belt from said first opening, said second air aperture comprising part of the means to predetermine the lateral displacement of said belt prior to reversal, said logic circuit means including means to cause air flow in an output circuit only when said second aperture is covered, and means connecting said output circuit to said means for displacing the axis of one of the rolls to cause said means for displacing the axis of one of the rolls to cause displacement of said roll in said second direction upon covering of said second aperture by said abrasive belt.
 3. The device of claim 2, said logic circuit including a bi-stable fluidic circuit element having two output ports which respectivelY emit air as a stable output mode after an associated control port has been supplied with air, and two control ports respectively connected to said fluidic circuit element to initiate said respective stable output modes when the respective inputs receive air, said logic circuit further including a respective fluidic circuit element connected to each said air aperture to supply said air to its respective control port only when said aperture is covered by said belt, the respective output ports of said fluidic circuit element being the portion of said logic circuit connected to said means for displacing the axis of one of the rolls, one said output port being connected to cause said displacement of one of the rolls in said first direction and the other said output port being connected to effect displacement in said second direction whereby each stable output mode causes displacemt of said belt in a respective direction.
 4. The device of claim 1 in which said predetermined lateral displacement is predetermined solely by the uncovering of said aperture by said abrasive belt.
 5. The device of claim 4 further including a monostable fluidic circuit element having one stable output mode and one unstable output mode and having an input port connected to initiate said unstable output mode only while said input port is receiving air, and means to supply air to said input port only when said belt moves laterally to partially block said aperture, each said output mode being connected to cause displacement of said roll axis in a respective direction.
 6. The device of claim 5 in which said aperture is the outlet of a cone jet.
 7. The device of claim 1, said control bar having a curved upper belt-contacting surface, said bar having a plurality of apertures extending through said surface at each edge of said belt, said apertures being selectively connectable to said control means to predetermine the limits of lateral displacement of said belt.
 8. The device of claim 1, said control bar having a curved upper belt-contacting surface, said bar being further provided with means for mounting a sensing unit containing said air aperture just out of contact with said surface and said belt, the mounting of said sensing unit being effective to predetermine the limits of lateral displacement of said belt.
 9. The device of claim 8, said mounting means including discrete mounting openings in the rear surface of said bar, and clamp means on said sensing unit to secure said unit in a selected aperture, said upper surface being interrupted above each mounting opening.
 10. The device of claim 8, said mounting means including a longitudinal slot in the rear surface of said bar, and clamp means on said sensing unit to secure said unit to the margins of said slot in a selected longitudinal position, said upper surface of said bar being interrupted at least above said position. 